There have been many attempts to employ recycled plastics in producing final products with sizable market segments, competitive prices, and economical processing techniques. Among other constraints are the restrictions involved in separating different kinds of plastics from their mixture. Attempts to utilize mixtures of plastics having similar physical characteristics have not been particularly successful because in general the resultant products are more expensive than competitive products made from other materials such as virgin plastics, and the properties achieved from products made with mixtures of recycled plastics have not justified their higher purchase prices.
This same trend also exists in the wood industry. By-products from wood processing such as particle boards are used mainly with thermoset polymers, and the usage of such products is hampered because of adverse effects of exposure to water, high humidity, and weathering, and the deficiencies in certain mechanical properties such as fracture toughness and nailing capability.
Approaches used in seeking to improve the cohesiveness of cellulosic materials and polymers such as thermoplastic resins have generally involved chemical treatment of the cellulose to introduce functional groups tending to produce better bonding with the polymer. Such treatments of course add materially to the production cost and consequent selling price.